试导出方程M(x,y)dx+N(x,y)dy=0分别具有形为μ(x+y)和μ(xy)的积分因子的充要条件.
试导出方程M(x,y)dx+N(x,y)dy=0分别具有形为μ(x+y)和μ(xy)的积分因子的充要条件.
du(x+y)=u'x*(1+y')dx +u'y(1+x')dy
=(u'x+u'y)dx+(u'y+u'x)dx
dM/dx+dM/dy=dN/dx+dN/dy
充要条件:d(M-N)/dx=-d(M-N)/dy
du(xy)=u'x(xy'+y)dx+u'y(yx'+x)dy
=(u'x+u'y)ydx+(u'y+u'x)xdy
M/y=u'x+u'y N/x=u'x+u'y
充要条件M/y=N/x